1. Field of the Invention
The present invention relates to a current clamp circuit to clamp a current, that is, to restrict an output current externally in an output current amplifier circuit using a current buffer IC.
2. Description of Related Art
According to an earlier development, an output current amplifier circuit using a current buffer IC (Integrated Circuit) has been put to practical use. FIG. 2 shows one example of the output current amplifier circuit using the current buffer IC. In FIG. 2, the output current amplifier circuit 20 comprises a current buffer IC 1, an operational amplifier 2, and a direct current (DC) power supply 3. A positive pole side of DC power supply 3 is connected to an input terminal on a positive side of the operational amplifier 2. A negative pole side of DC power supply 3 is grounded. An output terminal of the operational amplifier 2 is connected to an input terminal of the current buffer IC 1. An output terminal A on an output side of the current buffer IC 1 is connected to a load 7 and an input terminal on a negative side of the operational amplifier 2. The load 7 is composed of a load resistor 7A and a load power supply 7B.
Herein, the current buffer IC is an amplifier capable of amplifying an output current sufficiently. In FIG. 2, an output voltage of DC power supply 3 is supplied to the input terminal on the positive side of the operational amplifier 2. Thereafter, an output of the operational amplifier 2 is supplied to the current buffer IC 1. Thereafter, an output of the current buffer IC 1 is supplied to the input terminal on the negative side of the operational amplifier 2. Further, an output current from the current buffer IC 1 is supplied to the load 7 on the basis of a voltage between the output terminal A of the current buffer IC 1 and the ground.
However, in the output current amplifier circuit 20 according to an earlier development, using the current buffer IC 1, there has been a problem that the maximum output current of the current buffer IC 1 flows into the load 7 as a load current.
Further, in the output current amplifier circuit 20, when the output terminal of the operational amplifier 2 is connected to the load 7 directly without using the current buffer IC 1, there has been a problem that it is not possible to flow the sufficient load current into the load 7 because the output current from the operational amplifier 2 is limited generally. Consequently, it is necessary to connect the current buffer IC 1 to the output terminal of the operational amplifier 2 in order to flow the sufficient load current into the load 7.
The present invention was developed in view of the above-described problems.
An object of the present invention is to provide a current clamp circuit which can easily clamp a current, that is, can easily restrict an output current externally in an output current amplifier circuit using a current buffer IC.
In order to solve the above-described object, in accordance with one aspect of the present invention, a current clamp circuit for restricting an output current in an output current amplifier circuit for amplifying the output current by using an operational amplifier (for example, an operational amplifier 2 shown in FIG. 1) and a current buffer IC (for example, a current buffer IC 1 shown in FIG. 1), comprises:
a resistor (for example, a resistor 4 shown in FIG. 1) which is connected to an output terminal of the current buffer IC; and
an output current restriction unit (for example, two diodes 5 and 6 shown in FIG. 1) connected to the current buffer IC and the resistor in parallel, for restricting the output current.
The output current means a current which is produced by joining one flowing through the resistor from the output terminal of the current buffer IC to one flowing from the output current restriction unit. The current value of the current flowing through the resistor from the current buffer IC is determined by the voltage value of the voltage applied to the output current restriction unit, the resistance of the resistor, and the resistance of the current buffer IC. The current value of the current flowing from the output current restriction unit is determined by the current value of the rated load current of the operational amplifier.
According to the current clamp circuit having such a structure, in the current clamp circuit for restricting the output current in the output current amplifier circuit for amplifying the output current by using the operational amplifier and the current buffer IC, the resistor is connected to the output terminal of the current buffer IC, and the output current restriction unit for restricting the output current is connected to the current buffer IC and the resistor in parallel.
Preferably, in a current clamp circuit as described above, the output current restriction unit comprises two diodes connected to each other in parallel and in an opposite direction.
Preferably, in a current clamp circuit as described above, the output current restriction unit restricts an output current flowing from the current buffer IC through the resistor by a forward voltage value of either of the diodes.
According to the current clamp circuit as described previously, it is possible to easily restrict the output current externally in the output current amplifier circuit using the current buffer IC.